1. Field of the Invention
This invention relates to digital filters, and in particular to interleaved/retimed architectures for the lattice wave digital filter.
2. Description of the Related Art
In its most general form, a lattice wave digital filter (LWDF), which is one type of an infinite impulse response (IIR) filter, is composed of two branches of cascaded all-pass sections, as shown in the illustration in FIG. 1. A.sub.1 (z) is a first-order all-pass section and each of the other A.sub.n (z),B.sub.m (z) are second-order all-pass sections. Previous hardware implementations of the LWDF of FIG. 1 use the traditional structure (FIG. 2) or the bireciprocal structure (not shown) for the first- and second-order sections. While the traditional architecture can implement any filtering function, it has twice the hardware of the bireciprocal case. The bireciprocal filter is attractive in terms of hardware but is limited to halfband filtering functions. None of the previous approaches offers a solution that minimizes the hardware without restricting the transfer function characteristics. Thus, a problem with previous LWDF architectures is the trade-off between hardware size and transfer function characteristics. Accordingly, improvements which overcome any or all of these problems are presently desirable.